Maybe I am reading too much into things but:
Days of Future Past led into Days of Future Present
Days of Future Present was a massive cross over with X-Men, X-Factor, New Mutants and Fantastic Four...all are owned by Fox

as for cast I don't think anyone is a lock or not a lock to be in this:

we saw a X-men movie where Storm, Wolverine and Rogue were X-men before Angel and Iceman
we saw an Avengers team founded by Cap, Black Widow and Hawkeye (yes Cap is considered a founder but the original team was IM, Thor, Hulk, Antman/giantman and wasp)

__________________
Journeying to the Undying Lands in the West
So Long and thanks for all the fish

The way people have been *****ing about Hugh, Famke, Halle, Ian, and Patrick's ages over the last few months, you'd think they'd want to stay away from casting someone who'd be in his mid 60s when the film is released.

Jeff Wadlow, who is readying for the August 16 release of Kick-Ass 2, has been tapped to write an adaptation of X-Force, an X-Men spin-off being developed by 20th Century Fox.

The news comes on the heels of various blogs reporting today that the studio registered X-ForceMovie.com a few months ago.

Longtime X-Men franchise producer Lauren Shuller Donner is producing X-Force.
Wadlow is now writing the script with an eye to direct.

X-Force was an early 1990s spin-off from Marvel Comics’ flagship Uncanny X-Men comics created by Rob Liefeld and its first issue set sales records when it sold five million copies. (The record was only surpassed when X-Men #1, drawn by Jim Lee, sold eight million issues.)
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The original line-up of the team was made up of several characters from the first Uncanny X-Men spin-off, The New Mutants, teens who had matured into young adults. But also among the line up was Cable, a militant leader from the future who is related to X-Men heroes Cyclops and Jean Grey. His body is enhanced by robotic parts and he has some telekinetic powers as well.

Wadlow wrote and directed Kick-Ass 2, the sequel to the violent and funny 2010 hit based on the comic books by Mark Millar and John Romita Jr. He recently wrote two episodes of A&E’s hit show, Bates Motel.

Wadlow is also writing an adaptation of Bloodshot, based on the Valiant comic and set up Columbia.